Ashley Jones is only 34, but lately she feels like she's forgetting everything. "I never remember where I put my subway card," says Jones, an event planner in New York City. "I run out to the grocery store and come home without one of the three items I needed. I'm not a flake, but sometimes I'll forget commitments and friends' birthdays."

To be sure, Jones has a lot to juggle: She flies to a new state nearly every week to organize conferences for her tech-company clients. She's been known to send email while brushing her teeth. Still, she worries that her forgetfulness is about more than just her schedule. "I used to be a pretty efficient person," she says. "But lately, it's like, Where is my mind?"

For today's overbooked women, 30 can feel like the new 60. We may be running board meetings, start-ups and households—not to mention tweeting several times a day and hitting the gym a few times a week—but we can no longer recall whether we turned off the iron or where we put our car keys.

It sometimes seems like there's a fuzzy-brain epidemic. Scientists like Timothy Salthouse, Ph.D., director of the University of Virginia's Cognitive Aging Laboratory, are studying the brains of young people to see when negative changes are setting in. Surprisingly, certain aspects of age-related cognitive decline begin as early as our 20s and 30s. We're all so busy being present: How is it that we're so absentminded?

Cognition 101

In order to figure out why a growing number of healthy young women blank out at the ATM when punching in their PIN, it helps to understand the basics of cognition. Which is complicated: The brain is mysterious, even to neuroscientists who study it for a living. "It's not just the sheer complexity of the organ, it's also the variability from person to person," says Denise Park, Ph.D., distinguished university chair in Behavioral and Brain Sciences at the University of Texas in Dallas. Plus, little brain research exists on people ages 25 to 55.

Still, there's a lot we do know. Brain function can be divided into two categories: mechanics and pragmatics. Mechanic functions involve "information processing, memory, speeded responses, thinking quickly, and being able to reason, make judgments and solve problems efficiently," says Margie Lachman, Ph.D., a psychology professor at Brandeis University. Pragmatic functions, on the other hand, involve drawing upon accumulated knowledge and experience to make decisions.

In general, mechanics slow as we get older, while pragmatic function improves. "Women in their 20s and 30s are at the peak of their mechanics," says Lachman. "But pragmatic functioning peaks much later in life. Right now, you're just beginning to accumulate knowledge and experience."

Researchers believe that this continual gain may compensate for the slowing down of certain brain functions as we age. Similarly, some elite athletes who peak in their 20s still excel later in life: Years of practice and experience help them focus better, perhaps making up for losses in endurance and speed. Eventually, we all become slower and more forgetful, with the declines really picking up speed after age 65.

The trouble is that despite the knowledge we're racking up as young and middle-aged adults, we may be setting ourselves up for diminished brain capacity with certain lifestyle behaviors, including living in what can feel like a constant state of overdrive, hyperstimulation and being plugged in. (Busy is good for the brain; overwhelmed is not.) "The things that decline earliest are memory, reasoning and speed," says Salthouse. Fortunately, these normal changes do not signal early-onset Alzheimer's—but they're still unwelcome developments for women who are in their cognitive prime.

Here are three ways to give your memory a helping hand:

1. Stop multitasking.

For years, Kristi James, 36, had a demanding job as a university administrator in Tampa, Florida. She was regularly getting stuck trying to think of everyday words, and one time she didn't complete an important work assignment—because she totally forgot about it. "My memory has been bugging me for several years," she says. "And my processing time is just slower than it used to be."

James's daily schedule was intense: After coming home from her full-time job, she paid bills, sent email and worked as a volunteer enrollment director for the Ivy League college from which she graduated. "I probably spent 50 hours doing DIY projects for my son's first birthday party," she says. "I stayed up until 1 or 2 A.M. cutting paper and pasting things together." Now she's a stay-at-home mom, but James has traded one big to-do list for another. And she still has lapses: There are mornings she forgets to pack her son's lunch, or to bring his goggles to the pool.

For many women, cognitive chaos is less about the functionality of our instrument than about how we're playing it. Adulthood, after all, is a time when we're juggling a lot of responsibilities, many of them new. "You're approaching a high level of demand at work, you may have young children, you could have responsibility for your parents, and you have a very active social life, in addition to working long hours," says Park. "That adds up to a very high level of neural demand that may result in a feeling of cognitive depletion." When we're stretched this thin, it's likely lack of attention, not memory, that causes us to feel frazzled. "You're multitasking, you're distracted. You're thinking about one thing and doing another," says Park. "When you lose your keys, it's probably not because your mind is slipping. It's because you never knew where you put them in the first place."

The issue is that we have a finite amount of cognitive resources to apply, says Peg Dawson, Ed.D., coauthor of Smart but Scattered. "If we're using all of them to juggle multiple responsibilities, we just don't have enough left," she says. It doesn't help that we live with black holes of distraction perpetually at our fingertips: "Technology and smartphones are a big problem," says Gary Small, M.D., coauthor of 2 Weeks to a Younger Brain. He believes that technology isn't just distracting us, "It's altering our brain function." Experts have connected gadget use to increased stress and trouble focusing; a recent study by Dr. Small found that 11- to 13-year-olds who stopped using their gadgets for five days while at a nature camp showed significant improvement in tests of social and emotional intelligence. "Tech interferes with our human-contact skills," says Dr. Small. In other words, the stakes here are potentially much higher than absentmindedness.

2. Work out—for your brain.

Diet, stress, alcohol consumption, sleep and exercise—basically, all the things that affect our physical health—have been proven to impact our cognitive health, too. "Increases in cortisol, which is linked to stress, have been shown to have a direct effect on the hippocampus, which affects memory," says Lachman. Adds Dawson: "I suggest you step back and say, 'What can I do about the stress?' instead of 'What can I do about my memory?' "

Luckily, the brain is a resilient organ, and scientists agree that protecting your brain while you're young is one of the best things you can do to maintain your cognitive health. The number-one change many experts suggest? (Phew: It's not crossword puzzles.) "Exercise can really boost your cognitive abilities in a short time," says Dr. Small. "It can increase your brain size over six months or a year." This is likely because it keeps arteries flexible and increases blood flow to the brain. "If you have poor blood flow, it's possible that certain regions of the brain cannot be activated to their maximum potential," says Park. Exercise also causes the production of chemicals that promote sprouting of neuronal branches, facilitating communication between cells in the brain.

Now that she's not in the office five days a week, James is regularly walking her son to school with the dog—an hour round trip. "Being able to walk a few times each week has definitely helped," she says. "Exercise helps me feel less stressed." Diet is important, too. "Consume more omega-3 fats, and fruit and vegetables, and minimize processed foods, refined sugars and red meat," says Dr. Small. And it's no surprise that sleep is crucial: "A good night's sleep will increase your mental focus and lower inflammation in the brain," he says.

One remedy you've probably heard about is brain games. While many people believe in their effectiveness, scientists are divided over how much they actually help. At your current age, your brain probably is not suffering from lack of stimulation—most of us face enough mental challenges in our daily life that we don't need to play Word Scramble in our (nonexistent) spare time in order to improve our brain function. "Rather than boosting memory, I think brain games tend to make people better at a specific task," says Dawson.

3. Keep your reminder system updated and fresh.

In addition to healthy habits, there are easy ways we can help our brains help us. Park suggests thinking deeply about tasks you want to complete the next day before going to sleep, imagining yourself finishing them in detail. "There's something about creating a scenario in your head that greatly improves the probability you will actually complete that scenario," she says. (See "4 Easy Ways To Strengthen Your Memory," for more tips.)

Dawson cautions that the brain naturally seeks novelty—so you may have to switch up your methods every few months if they stop working. "You don't want to use the same system again and again, because the brain gets used to it," she says. Her preferred memory triggers currently include colored Post-its, a wipe board in her kitchen and placing things she needs to take to work right in front of the door, where she'll trip over them. She doesn't make these accommodations because her mind isn't sharp, but because it has more important things to think about. "Generally, our brains are efficient," says Dr. Small. "If you're a mathematician, you'll remember your calculations, but you don't need to remember people's names. What's important to you, you will remember."